The present invention relates to an aqueous system for applying a drafting composition to the surface of a substrate to provide a drafting film and, more specifically, to an aqueous coating composition for a hydrophobic sheeting material which is also compatible with a diazo light-sensitive coating composition.
Support substrates prepared from hydrophobic resins, such as polyester resins, have proved highly satisfactory for use in the manufacture of reprographic film products. Matte-surfaced polyester sheeting material has found wide acceptance as specialty materials in engineering, drafting and related uses. Such matte-surfaced polyester sheeting may be used as a member on which ink and pencil drawings can be made or it can be overcoated with a suitable light-sensitive emulsion to provide a reprographic film product for use in graphic reproduction art. The coating of a drafting lacquer onto a film base from conventionally used solvent systems to provide the drafting properties of the coated film has not only proved to be costly due to the use of the organic solvents, but the solvents used present safety hazards and have a negative impact upon the environment such that expensive solvent recovery systems must be utilized to dispose of the solvents by environmentally accepted procedures. The substitution of aqueous coating systems in place of conventional solvent systems has major advantages due to their environmental considerations, safety and cost requirements. The use of waterborne systems eliminating the need for solvent recovery greatly reduces the problems of waste disposal. However, the coating of a drafting lacquer onto a film base from an aqueous emulsion rather than the commonly used solvent systems is not without its disadvantages. The coating produced from a waterborne system does not readily adhere to or coat evenly the surface of a hydrophobic material which intrinsically repels water. Furthermore, it is difficult to find waterborne resins capable of providing the desired drafting properties and, at the same time, be compatible with a reprographic film coated thereover, particularly a diazo imaging composition.